Recent technological advances in light microscopy, video camera design, and digital image processing have made it possible to observe biological processes that were previously invisible. The equipment requested in this application will be used for this purpose. It will be shared by eight users in five departments of the Medical School. The research projects, which cover a wide spectrum of biological problems, cannot be performed without this equipment, which is otherwise unavailable to the users. Some projects will involve the use of specific molecules (fluorophores) whose fluorescence will provide a measure of a cell's electrical activity, or the amount of important cell constituents, such as particular ions or cell surface molecules. To avoid damaging the cells with light, and to detect very low amounts of fluorescence, a video camera which intensifies the image must be used. In addition, digital processing will enhance the contrast of the image, and will be used to quantify the level of cell constituents under study. Other projects will not require fluorescence microscopy or low light levels. Instead, these will use differential interference (DIC) microscopy to achieve a very high spatial resolution of the cells being studied. Digital image processing will further enhance the spatial resolution. Subcellular constituents, invisible with ordinary microscopy, will then be observed. In both types of experiments (fluorescence and DIC microscopy), specific hypotheses about the expression, movement, disposition, and organization of cell specializations will be tested. Included are studies of cell migration, neurite extension, microtubule and vesicle movement, ion pump and channel distribution, and expression of specific proteins in neurons.